The invention relates to an MR (Magnetic Resonance) coil module for use in an MR imaging system for receiving and/or transmitting RF (Radio Frequency) signals. The invention relates further to an MR imaging system comprising an RF coil system for transmitting and/or receiving RF signals.
The article xe2x80x9cSENSE: Sensitivity Encoding for Fast MRIxe2x80x9d, Klaas P. Pruessmann et al., Magnetic Resonance in Medicine 42:952-962 (1999) describes a concept for considerably enhancing the performance of magnetic resonance imaging (MRI) by means of arrays of multiple receiver coils. Therein sensitivity encoding (SENSE) is described which is based on the fact that receiver sensitivity generally has an encoding effect complementary to Fourier preparation by linear field gradients. By using multiple receiver coils in parallel scan time can be reduced and resolution can be increased.
In practice different kinds of receiver and/or transmitter RF coils are required for MRI in a very short time frame depending on the particular application, e. g. depending on the size and the location of the region of interest. It is thus an object of the present invention to provide an MR coil module which is usable for different applications in an MR imaging system and has better SENSE capabilities, in particular a higher SENSE factor, i. e. allowing an increased scan time reduction when using the described SENSE method.
This object is achieved by an MR coil module for use in an MR imaging system for receiving and/or transmitting RF signals, the coil module including at least two coil elements positioned next to each other, a preamplifier for each coil element, a signal bus for transferring RF signals between said coil elements, an output means and an input means, an output means for outputting RF signals from the MR coil module, an input means for inputting RF signals into the MR coil module, switching means for switching the connections between said coil elements, said input means and said output means, wherein said output means and said input means are adapted complementary so as to enable electrical and mechanical connection of the module to other modules.
The invention is based on the idea to provide identical MR coil modules which can be used stand-alone or in combination with other, identical modules to increase the region of interest which can be covered. By using identical coil modules higher volumes in production can be achieved thus reducing the costs for development and production. In addition, development time is shorter since otherwise several different coils need to be developed in parallel. The user can start with a small set of coil modules and expand later to full coverage. Also if one module is not working, the other modules are still available for use. Since coils with a large coverage are necessarily big and difficult to handle, the coil modules according to the invention can be put on a patient support one by one thus making the handling easier.
According to the invention output means and input means are provided for outputting and inputting, respectively, RF signals and, at the same time, for electrically and mechanically connecting the module to other modules if required. Each module consists of a number of coil elements, the maximum number of coil elements being limited to the number of channels the MR imaging system can read out simultaneously. A signal bus is introduced, preferably as wide as the MR imaging system has simultaneous channels. Further, switching means are provided for connecting and disconnecting the signal bus of a module to the signal bus of other modules. When the module is connected to the MR imaging system but not used for scanning it should be disconnected from the signal bus so as not to interfere with other modules.
The preamplifiers are included in the coil module and located between the coil elements and the switching means, preferably close to each related coil element. Thus a good Signal-to-Noise ratio can be achieved.
According to one embodiment of the invention an MR coil module comprises at least two coil elements positioned next to each other without overlap, preferably when using SENSE coils. It has been found that an optimal SENSE coil providing an increased SENSE factor which is the factor by which the time duration of the scan is reduced by using the SENSE method, has no overlapping coil elements. In addition, it has been found that the exact location of the coil elements to each other is not very critical. The SENSE factor is, in general, determined by the number of coil elements which can receive signals in parallel independently. The more coil elements are available, the higher the SENSE factor.
To improve mechanical connection of the module to other modules mechanical connection means are provided. Such mechanical connection means may include snaps and/or flaps, which are preferably used in a flexible coil solution. By use of an additional flap on each module the module can be attached to the next module using Velcro. Alternatively, coil elements and coil modules could also be positioned simply next to each other without mechanical connection since, according to the invention, the exact location of the coil elements to each other is not very critical.
In another aspect of the invention output interface means and/or input interface means are provided for translating signals of the MR imaging system to signals of the MR coil module. Said interface means are preferably integrated into each MR coil module. However, said interface means could also be part of the MR imaging system. According to a preferred embodiment the switching means are adapted for connecting either said input means or said coil elements with said output means in order to prevent an interference of different signals on the signal bus. By said switching means a time multiplexing of different signals can be achieved.
The switching means may further include a switching element for each coil element which is adapted for connecting either said coil element or a corresponding input line of said input means with a corresponding output line of said output means. Thus, it can be selected, if signals from each single coil element of a coil module shall be transferred to the signal bus and to the output means or not.
In a further embodiment a module identifier is provided in each MR coil module. Said module identifier enables the MR coil system to identify which and how many MR coil modules are connected to the MR imaging system.
By combining several coil modules according to the invention several coil configurations can be made. For enabling the MR imaging system to know which configuration is used a resistor is provided in each coil module. When several coil modules are chained to each other these resistors are connected in parallel and the total resistance at the output of the first coil module decreases. The total resistance is thus a measure for the number of coil modules connected. It is also possible that the above mentioned interface means can translate the value of the resistance of several resistors connected in parallel when connecting several modules to a specific coil identifier allowing to identify the specific coil modules configuration.
The invention relates also to an MR imaging system comprising an RF coil system for transmitting and/receiving RF signals, said RF coil system including at least two identical connected MR coil modules as described herein.